The present invention relates to a process for lacquering objects with a multi-layer lacquering containing a layer of base lacquer and a layer of clear lacquer on top of this, the base lacquer containing at least one nacreous pigment based on mica flakes coated with metal oxides.
Nacreous pigments have hitherto been used for a number of applications, in particular in cosmetics. Nacreous pigments have also been proposed for use in automobile lacquers; however, it has not yet been possible to achieve a wide application in this field, despite the particularly interesting and attractive lacquerings made possible because of the optical properties of nacreous pigments. Apart from the fashion considerations, this is due to the particularly high quality requirements imposed on automobile lacquers, which, according to their intended use, are in some cases exposed to extreme weather conditions over long periods of time.
The color of nacreous pigments based on mica flakes coated with metal oxides is based on interference phenomena in the reflection of the incident light at the thin layer of metal oxide. Since the interference depends on the angle of the incident light or the viewing angle, as far as possible, the pigments must be aligned parallel in the layer of lacquer. It is also known that diffuse light scattering leading to a whitening of the color and to a loss in gloss and color intensity occurs at each corner or edge of a pigment particle. Both plane-parallel alignment of the pigment particles, which must take place at the moment at which the lacquer is applied to the surface to be lacquered, and the gloss and tinctorial strength of the pigments are favored by using pigment particles with a relatively large main diameter.
Thus, above all, nacreous pigments with particle sizes of about 10-70 .mu.m, most of the particles being in the order of size of about 30 to 50 .mu.m, have hitherto been used in lacquers and paints in which high gloss and high tinctorial strength were desirable. Although these pigments are particularly suitable for very many applications, nevertheless, surprisingly, the results obtained when they are used in automobile lacquers are not good. Rather, where polycondensation systems customary in series lacquering are used, it is found that customary nacreous pigments produce lacquers with a poor clear lacquer quality and a relatively rough surface which therefore has poor gloss.